I'm trying to remember a word, I think it's related to computational or database theory. The closest synonym is
atomic but that's not exactly it. Basically it's a kind of computation that should produce the same result even when run multiple times in a row, meaning it doesn't create side effects for itself.
I specifically ran across this word in a Stack Overflow answer about a chmod command (or some other permission related operation).
Hopefully that's enough to go on. Poking around Wikipedia isn't much help.